Movable graduator



Aug. 18, 1959 M. McwHlRTER E1' AL 2,899,749

MovABLE GRADUATOR yFiled sept. l1ra. 1955 F/G. I

A Trae/V5 Ys United States Patent 2,899,749 MOVABLE GRADUATOR Milford McWhirter and Wayne T. McWhirte'r, Arlington Heights, lll.

Application September 16,1955, Serial No. I534,748

1 Claim. (Cl. 33-75) This invention relates to drafting instruments, and more particularly to a drafting instrument that is intended to aid a draftsman in laying out graduations or segments of a circle or dial.

Heretofore, the conventional method of drawing dials, gears, or any circular ligure requiring the laying out of radial lines angularly spaced about the circumference of said figure predetermined distances apart, has been to line up a straight edge with the center of the previously drawn circle or dial and with the periphery of the graduated circle, after which the desired line is drawn.

This method entails considerable inconvenience and loss of time so far as the draftsman is concerned, and the main object of the present invention, accordingly, is to obviate the diiculties which have heretofore persisted, by providing a specially designed instrument which will facilitate the laying out of graduations or segments of a previously drawn circle or dial.

A more specific object is to provide a device of the character referred to which will be so designed as, when set in a position to permit the drawing of the line, to be bodily ladjustable in a transverse direction to an extent that will compensate for the thickness of the line. f The purpose here is to insure that a straight, radially extending ink line will be exactly located and will, due to the compensation for its thickness,v be exactly centered in respect to a previously drawn pencil line.

Another specic object of the invention is to provide a device as stated which will be readily usable in laying out radial lines or segments of a drawn circle or dial, without the necessity of marking the drawn circle orf in degrees. In use of the invention, it is merely necessary that a movable arm constituting. `a part of the drafting instrument be registered with a selected degreemarking of a disc also constituting part of the instrument, after which the radial line may be drawn.

Still another object is to provide a device as stated which will be readily usable not only by draftsmen for drawing dials, gears, and the like, but also by tool makers in laying out lines extending accurately and directly from a common center.

Other objects will appear from the following description, the claim appended thereto, and from the annexed drawing, in which like reference characters designate like parts throughout the several views, and wherein:

Figure l is a top plan view of a drafting instrument formed according to the present invention, a portion of the movable arm being broken away;

Figure 2 is a longitudinal sectional view on line 2-2 of Figure l;

Figure 3 is an enlarged transverse sectional View on line 3 3 of Figure 1; and

Figure 4 is an enlarged fragmentary top plan view of the disc.

The reference numeral has been applied toan elongated, straight arm, one longitudinal edge 12 of which comprises a straight edge along which la line may be drawn. -V

At one end, arm 10 has an upwardly offset portion 14, formed with a disc shaped enlargement 16 projecting laterally beyond the straight edge 12 of the arm and centrally formed with a closed slot 18 extending transversely of the arm, in perpendicular relation to straight edge 12, the straight edge being extended along a line intersecting perpendicularly with slot 18 medially between opposite ends of the slot.

The instrument further includes a disc 20 of a diameter substantially greater than that of enlargement 16, having a beveled marginal portion 22 provided with radially extending markings 24 that are associated with numerical indicia as shown in Figure 4, calibrating the periphery of the disc in degrees of a circle. As shown in Figure l, the main markings 26, 28 are provided on the disc, these markings extending over the full diameter of the disc and intersecting at the center thereof, these marking designating zero degrees, degrees, 180 degrees, and 270 degrees respectively. The remaining markings are short, terminating in closely spaced relation to the periphery of the disc and as shown in Figure 4 may be of different lengths to provide main subdivisions of the calibrated disc periphery, Such as 5 degrees, l0 degrees, etc.

Referring to Figure 3, disc 20 is formed with a center opening 30, and extending 'through said center opening is a pin 32 havinga flat head defining a shoulder 34 extending circumferentially of the pin, opening 30 being counterbored to receive said head.

Pin 36 is formed with a reduced, upwardly projecting threaded extension 38, extending through a slot 18, and threadable onto the extension is a capnut 40, bearing against a washer 42, which is interposed between the top surface of the arm and the cap nut. n

To facilitate registration of straight edgeK 12 with a selected marking 24, 26, or 28 of the disc, enlargement 16 has a notch or indentation 44 where straight edge 12 meets the edge of the enlargement, through which indentation a selected main marking 26, 28 of the disc may be viewed. l.

v That portion of arm 10 that projects outwardly beyon the periphery of the discrhas a flat underside lying in a plane closely spaced above and paralleling theY plane of the at underside of disc 20. T o maintain the projecting portion of the arm in thisl position, the arm at its free end has a downwardlystruck, rounded projection 46 engaging the surface of the work W. Y

In use, the disc is secured centrally to the drawing with a Suitable length of tape, not shown, and nut 40 is backed oi slightly. This permits free swinging movement of the Iarm about the axis of the pin, toy dispose straight edge 12 in registration with a selected radial marking of the disc. The line may now be drawn, and it will be seen that by making successive adjustments in the position of the arm, a plurality of lines extending radially from a common center will be drawn, with said lines being angularly spaced about said center selected distances apart. I-n this way, the graduation of a drawn circle or dial is measurably facilitated, and the previous method heretofore followed, of lining up a straight edge with the center and outer part of the circle being graduated, and then drawing the line, is eliminated.

The provision of the slot facilitates the drawing of ink lines of selected thickness. Assuming, for example, that the dial has been laid out in pencil, in inking the drawing one first adjusts arm 10 to a position in which its straight edge 12 is registered with a previously drawn pencil line. Then, with the nut slightly loosened, the arm is bodily adjusted in a transverse direction, longitudinally of slot 18, to slightly offset the straight edge 12 radially of the disc. This compensates for the thickness of the ink line that is to be drawn, and eliminates the possibility of a relatively thick ink line being drawn wholly to one side or the other of the previously drawn pencil line. The accurate laying out of the dial or circle, both when the drawing is being penciled and when it is being inked, is thus assured.

The construction of the instrument is such as to permit one to lay out a circle in segments without the necessity of rst marking off the periphery of the drawn circlel at selected locations angularly spaced about said periphery. One may, in fact, place the disc at the approximate location desired on the work surface, and draw all the radial lines that are being used to graduate a dial. Then, the disc can be removed, and by extending two or more of said lines radially, inwardly until they intersect, one may nd the center of the dial, and may then proceed to draw the dial itself about said center.

The purpose of maintaining the arm out of full contact with the work surface, of course, is to eliminate the possibility of accidental movement of the arm over an ink line that is still wet, which would cause smearing of the work, the construction being one that permits rapid adjustment of the arm across wet lines without fear of smearing the same.

It is believed apparent that the invention is not necessarily confined to the specific use or uses thereof described above, since it may be utilized for any purpose to which it may be suited. Nor is the invention to be necessarily limited to the specific construction illustrated and described, since such construction is only intended to be illustrative of the principles, it being considered that the invention comprehends any minor change in construction that may be permitted within the scope of the appended claim.

What is claimed is:

A drafting instrument of the type described, comprising: an elongated, straight arm one longitudinal edge of which is adapted to provide a straight edge along which a line may be drawn, said arm beingl formed at one end with an upwardly offset portion having a circular enlargement formed centrally with a straight slot the length of which extends normally to the length of the arm, said slot being intersected medially between opposite ends thereof by a straight line drawn in extension of the straight edge across said enlargement, said straight edge constituting one longitudinal edge of the arm and the other longitudinal edge of the arm being extended tangentially to said enlargement, said straight edge being extended radially of said enlargement, the arm being formed adjacent the extremity thereof remote from the enlargement with a rounded projection on the underside of the arm adapted to ride upon a support surface, the upwardly offset portion being connected to the remaining portion of the arm by a sloped part inclined slightly from the horizontal; and a support disc underlying the upwardly olset part of the arm, said disc having a beveled peripheral portion, the slope of which matches the inclination of said sloped part, said beveled portion underlying said slopedV part, the disc having, inwardly from said beveled portion, a at top surface extending in parallel relation to the undersurface of the upwardly offset part, the top surface of the beveled marginal portion of the disc extending in parallel relation to and underlying the bottom surface of the sloped part of the arm, the remaining part of the arm having a bottom surface parallel to the bottom surface of the upwardly offset part and adapted to extend parallel to a work surface from which it is spaced by the rounded projection; and a pin pivotally *connecting the arm to the disc, said pin projecting upwardly, centrally through the disc and including a shoulder spaced a short distance upwardly from the top surface of the disc in contact with the underside of the upwardly offset portion of the arm, said shoulder supporting the upwardly offset portion of the arm abovethe top surface of the disc a distance equal to that between the underside of the sloped part and the -top surface of the beveled marginal portion of the arm, said distance also being equal to the distance that the underside of the remaining portion of the arm is spaced upwardly from the work surface by the rounded projection, the pin having a reduced portion extending upwardly from the shoulder through the slot and threaded at its upper end; and a nut threaded upon the upper end of the reduced portion of the pin and constituting means for holding the arm and disc assembled with each other with the upwardly olset portion of the arm in contact with the shoulder of the pin.

References Cited in the Ele of this patent UNITED STATES PATENTS OTHER REFERENCES Cassell Company Publication, received in U.S. Patent Ofce September 20, 1946, 1 p. 

